In electric vehicles, i.e. in vehicles that are driven electrically, the rechargeable battery that is present for driving the electric motor is utilised for supplying various auxiliary units, i.e. electric consumers, with electric energy. Since in electric vehicles no waste heat generated by an internal combustion engine is available for heating the vehicle interior, an electrically operated heating device is required which likewise draws its electric power required for the operation from the battery of the electric vehicle. However, this electric energy is no longer available for driving the electric motor, which can significantly reduce the range of the electric vehicle.